Geometries and dissociation energies of water molecules on Ga doped Al clusters were investigated using the first-principles density functional PW91 method.This work is divided into two parts: (i) the equilibrium structures and stability of AlnGa (n=2-15) clusters and (ii) the interaction of H2O with stable AlnGa clusters.The results reveal that the most stable AlnGa structures have similar configurations as the most stable host Aln+1 cluster except Al4Ga.